High power density requirements in III-Nitride lasers and light-emitting diodes, transistors, and solar cells has led to the demand for solid state cooling technology, in particular, for nitride-based alloys that can be integrated with GaN devices. In recent years thermoelectric devices have drawn significant attention due to their use in electronic cooling and heat recycling for electric power generation. A thermoelectric device creates a voltage when there is a different temperature on each side of the device. Conversely when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect). This effect can be used to generate electricity, to measure temperature, and to heat or cool objects. Because the direction of heating and cooling is determined by the polarity of the applied voltage, thermoelectric devices make very convenient temperature controllers.
Much materials and structures research has been undertaken with respect to thermoelectric devices and the number of device applications has grown dramatically. The thermoelectric and device cooling applications of III-Nitride based alloys is yielding some promising results because they are non-toxic, highly thermally stable and radiation proof. III-Nitride devices in particular have been widely applied in high power, high temperature environments, and efficient thermal management is required for such broad applications in photonics, optoelectronics and electronics.
The thermoelectric properties for RF-sputtered AlInN have been reported (see, e.g., S. Yamaguchi, Y. Iwamura, and A. Yamamoto, Appl. Phys. Lett., 82, 2065 (2003); S. Yamaguchi, R. Izaki, K. Yamagiwa, K. Taki, Y. Iwamura, and A. Yamamoto, Appl. Phys. Lett., 83, 5398 (2003); S. Yamaguchi, R. Izaki, N. Kaiwa, S. Sugimura and A. Yamamoto, Appl. Phys. Lett., 84, 5344 (2004); and S. Yamaguchi, R. Izaki, Y. Iwamura, and A. Yamamoto, Physica Stat. Solidi (a), 201, 225 (2004)), as have the thermoelectric properties for MOVPE-grown InGaN (see, e.g., B. N. Pantha, R. Dahal, J. Li, J. Y. Lin, H. X. Jiang, and G. Pomrenke, Appl. Phys. Lett., 92, 042112 (2008), and B. N. Pantha, R. Dahal, J. Li, J. Y. Lin, H. X. Jiang, and G. Pomrenke, J. Electro. Mater., 38, 1132 (2009)).
AlInN prepared by an RF-sputtering method (leading to polycrystalline AlInN material) results in a material that has a poor Z*T value (=0.005, T=300K), which is unacceptable for thermoelectric devices. MOVPE-grown InGaN results in a single crystal InGaN material that has a poor Seebeck coefficient, which is also unacceptable for use in thermoelectric devices.